Continuous upflow digester



P 1965 L. A. CARLSMITH 3,206,356

CONT INUOUS UPFLOW DI GE 5 TER Filed June 5, 1964 United States Patent3,206,356 CONTINUOUS UPFLOW DIGESTER Lawrence A. Carlsmith, Amherst,N.H., assignor to Improved Machinery Inc., Nashua, N.H., a corporationof Delaware Filed June 5, 1964, Ser. No. 372,907 3 Claims. (Cl. 162237)This is a continuation-in-part of my application S.N. 198,558 filed May29, 1962, which is in turn a continuation-in-part of my application S.N.805,503, filed April 10, 1959, both now abandoned.

This invention relates to the production of pulp from wood chips andmore particularly to novel discharge apparatus and methods for acontinuous upflow digester, capable of cooking wood chips at hightemperature and pressure, draining the cooking or other liquor from thechips while maintaining them at high temperature and under pressure, andthereafter cooling and discharging to atmospheric pressure withoutflashing the so treated and drained wood chips by adding fluid theretoto aid such discharge.

The discharge of the treated wood chips from a continuous upflowdigester of the type shown in Patent No. 2,878,116 has proved to be aproblem because of its effect on the operation of the entire digestersystem as well as upon the treated wood chips themselves and their theirsubsequent treatment processes. Such a continuous digester may operateat high temperatures and pressures up to 350 degrees F. and 135 p.s.i.steam pressure under typical conditions, and with a digester vessel ofthe order of feet in diameter and 100 feet in length, produce, say 200to 300 tons per hour of pulp on air dry basis. Under such conditions,loss of steam which occurs upon discharge of the wood chips intoatmospheric pressure is a serious economic consideration, as is thereduction in fiber strength which may be caused by the sudden pressurereduction which occurs during such discharge. But some of the factorspresent in continuous digestion are, to a degree, in conflict, in thatthe nature of the chemical process for optimum efiiciency requires ashigh a cooking temperature and hence pressure as possible, but at suchhigh pressure the sudden release of the cooked wood chips from thepressurized digester into atmospheric pressure causes the liquorcontained in the wood chips and fibers thereof to flash and so damagethe fibers by rapid steam release therefrom. Nevertheless the use of alower cooking temperature necessary to avoid such flashing would bedetrimental to the cooking process.

According to the present invention, novel continuous pulping dischargeapparatus and methods are provided which solve the above recitedproblems in a unique manner. Specifically, the present inventionprovides a discharge system for wood chips treated in an uprightpressurized elongated reaction or other treating vessel of the typeshown in Patent No. 2,878,116, for example, including an uprightelongated pressurized wood chip receiver vessel having a substantiallysmaller cross sectional area than that of the reaction vessel in therange of about 10-50 to 1 but having its upper end in free pressurecommunication with the upper end of the reaction vessel. As shown insaid patent, means are provided for feeding substantially continuouslyinto the lower end of the reaction vessel a wood chip-liquid mixture tomaintain a compacted mass of wood chips within an elongated zone in thecentral and opposite upper end portions thereof and for advancing thewood chips upwardly through said zone at a rate substantiallyindependent of the movement of liquid in said vessel to treat said woodchips at high temperature and pressure, as well as liquid level controlmeans for establishing and maintaining a discrete level in the upperportion of said reaction vessel. Heating 32%,356 Patented Sept. 14, 1965and pressurizing means are provided for maintaining at least the upperportions of the interior of said vessels at a high temperature,substantially in excess of 212 degrees and at a pressure generally leastas great as p.s.i., substantially in excess of atmospheric pressure.

In accordance with the principles of the present invention, theelongated upright configuration and relatively small diameter of thereceiver vessel is important in order that a wood chip storage zonehaving stable temperature environment may be created with the topportion of the remover vessel at high temperature while the bottom mayremain at a much lower temperature, even less than 212 degrees F. Theinvention additionally provides conveyance means extending between saidvessels adjacent the upper portions thereof for establishing andmaintaining a predetermined level of the top of said mass of wood chipsabove the discrete level of said liquid in said reaction vessel,providing a drainage zone wherein is removed a substantial portion ofsaid liquid from said wood chips producing a high consistency thereof ofabout 2535 percent. The conveyance means moves drained cooked wood chipsfrom the reaction vessel to the wood chip receiver vessel wherein isestablished and maintained a vertically elongated storage zone of highconsistency drained cooked wood chips therein, as by means of suitablelevel sensors and controls. The elongated receiver vessel thus in eifectacts as a reservoir of wood chips, in that any non-uniform output fromthe conveyance means may be temporarily stored therein. It also makespossible the establishment of a temperature insulating zone by reason ofsaid elongated zone of stored treated wood chips, which permits a hightemperature to be main tained at the top of the receiver vessel, while alow temperature may be maintained at its bottom end. This makes ituniquely possible to cool the treated wood chips by adding a suitablefluid thereto at said bottom end, preferably a pressurized cool liquidsuch as water or dilute liquor to provide a cool, somewhat more dilutezone at the bottom of the receiver vessel to prevent flashing of thewood chips upon depressurizing at discharge.

The invention also provides means and methods for removing anddepressurizing the cooled but still pressurized wood chips directly fromthe lower end of said zone of high consistency wood chips in saidreceiver vessel into a substantially lower pressure zone, generally atatmospheric pressure, Without flashing, of the liquid in the pressurizedchips. More specifically, such means includes a wood chip dischargeorifice adjacent the lower end of the wood chip receiver vessel fordischarging pressurized wood chips therefrom, and, preferably, agitatormeans mounted for rotation within the lower end of the wood chipreceiver vessel. The agitator means operates to wipe the orifice and tomix the cool liquid or other fluid introduced through a suitable inletwith said wood chips immediately prior to their discharge in the cooledrelatively short and more dilute wood chip zone below said zone of highconsistency to aid in their discharge by diluting said wood chips withsaid added fluid, and, as is generally desired, to reduce thetemperature of the wood chips to less than 212 degrees prior to theirdischarge into said lower pressure zone to prevent substantial flashingthereof.

The novel vertical digester-receiver combination of the invention,particularly with an agitator at the bottom for maintaining the woodchips at an agitated state, and equipped with a restrictive dischargeorifice adjacent the bottom, has been effective in limiting steam loss,in that a temperature low enough to prevent flashing may be establishedtherein by the addition of cool liquid or other fluid, even though thetop of the receiver is maintained at a much higher temperature. Theagitator by itself maintains an efiicient discharge of the wood chipswhen supplied at a steady rate by the conveyance means, with the pulpbeing maintained at a predetermined level at the top of the storage zoneas the steam pressure on the top surface of the wood chips partlyfilling the receiver forces mobile stock through the orifice. But whenan unduly high level of wood chips due to an unusually high rate ofconveyance burdens the agitator, it has been difficult to maintain thedesired operation. The reason for this effect is that with a large depthof wood chips in the receiver as may occur from time to time with anon-uniform discharge from the reaction vessel, most of the pressuredrop between the steam pressure on the top surface of the storage zoneof wood chips and the pressure on the discharge side of the orificeoccurs across the depth of said storage zone. This pressure drop forcesthe wood chips downwards, compacting them. The compacted zone of highdensity wood chips offers an extreme resistance to agitation, due to adecrease in mobility. By the downward pressure, this dense mass isjammed down upon the agitator overloading its driver, ultimatelystalling it. When this happens, the orifice plugs,.since the wood chipsare no longer agitated. In fact, the wood chips compact so tightly thatno practical increase in driver power can provide for proper operationof an agitator-orifice discharge. However, as taught by the presentinvention the introduction of the pressurized fluid adjacent the lowerend of the receiver uniquely makes it possible to discharge from thereservoir of wood chips temporarily stored in the receiver, even thoughthere may be serious variations in wood chip flow into the receiver,such being aided by control of the orifice and fluid by level sensingmeans. This aspect of the invention also reduces the power requirementsof the agitator driver to permit the use of an economically feasibleelectric motor, and makes possible automatic load compensation of arotating agitator subjected to variable flow of wood chips from thebottom of the receiver.

The present invention, then, in one significant aspect, comprises meansfor admitting to the bottom zone of an elongated receiver vessel,directly connected to a reaction vessel for receiving drained wood chipsat high temperature and pressure therefrom, a controlled quantity of lowviscosity fluid under sufficient pressure to buffer the downward pulploading forces imposed on an agitator in response to conditions whichtend to halt the operation of the agitator-orifice in order to maintaindischarge thereof, such quantity and the discharge orifice opening beingunder the control of a level sensor if desired.

Another significant aspect of the invention comprises the use of a cooldilute liquor or water as the added fluid, in order to cool the drainedwood chips in a zone at the bottom of the receiver to a temperaturebelow about 212 degrees F. to prevent fiber damage caused by flashing ofthe wood chips upon their discharge to atmospheric pressure.

Other objects of this invention will be apparent from the followingdescription of the invention, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a partially broken away, partially sectional elevation of apreferred embodiment of the invention, showing a vertical upflowdigester according to the present invention;

FIG. 2 is a magnified sectional view of a portion of the digester ofFIG. 1; and

FIG. 3 is a schematic view of a unique automatic control system adaptedto be combined with the digester of FIG. 1 to effect automatic operationthereof.

A preferred embodiment of the apparatus of this invention, as shown inthe drawings, includes as its major components an upright pressurizedwood chip reaction vessel 22 in combination with a similarly pressurizedWood chip receiver vessel 48, with a conveyance 44 for feedingtherebetween at their upper ends. The receiver vessel 48 is of muchsmaller cross section area than is the reaction vessel of the order ofabout 1050 to 1, preferably about 20 to 1 as shown, and has an upwardfacing bladed agitator 50 rotatably mounted at its bottom and providedwith an electric motor agitator driver 52. A discharge orifice 56 havinga control valve 60 and associated controller 61 is positioned in thebottom zone of the receiver vessel 48 preferably beneath the agitator 50through which orifice agitated wood chips are forced from the vessel 48by pressure therein with little loss of steam while the bladed agitatorperiodically wipes by the entrance to the orifice. A lower inlet forpressurized fluid is provided in the bottom zone of the receiver vessel48 and is spaced from the discharge orifice 56, while an upper inlet 72may be positioned thereabove. A source of pressurized fluid is connectedwith the inlets 70, 72 through their valves 71, 73 respectively inseries with a valve 74 or 75 positioned in the line of flow source toinlet for controlling the pressurized fiuid. A level sensor 53 havingconnecting wires 55 is preferably provided for actuating the valve 71 or73 and orifice valve controller 61. Alternatively, there may be provideda motor load responsive means for operating said valves, which comprisesan electrical power responsive monitor operatively connected with themotor power lines and adapted to generate a signal indicating the amountof electrical energy being consumed by the motor, and the valves beingresponsive to the thus generated signal to control the flow of thepressurized fluid or the orifice opening. Commonly, valve 73 and inlet72, if used, maintain a constant fluid flow, with valve '71 being variedby the level sensor or the motor load responsive means.

In FIG. 1 is shown a wood chip reaction vessel 22 of the type describedin detail in Patent No. 2,878,116. A strainer 43 having a level or othercontrol valve 45 is located near the top of the reaction vessel todefine the upper liquid level therein at 23 and to define the bottom ofa drainage zone 66 thereabove so that the cooked wood chips may bedrained prior to their removal from the reaction vessel by conveyance44, to provide a consistency of about 25-35 percent. Heating andpressurizing means, such as heater 25 is also provided. As described insaid patent, the means for feeding continuously into the lower end ofsaid reaction vessel a wood-chip liquid mixture to maintain a compactedmass of wood chips within an elongated zone 46 in said vessel and foradvancing the wood chips upwardly through said zone at a ratesubstantially independent of that of the cooking liquor in said zoneincludes a foraminous screw means mounted for rotational andreciprocatory movement through a limited distance relatively to thelength of the vessel within the reaction vessel 22 near the lower endthereof by means of a shaft 30 extending vertically through the bottomof said vessel generally axially thereof. More specifically, saidforaminous screw means comprises a single turn helical plate 32 havingtherein a plurality of perforations 34 sufficient in number to allowsubstantially free passage of the liquid therethroug h but of smallenough size to prevent passage of wood chips or other fibrous material.The step of such helical surface is closed by a fiat plate 36 extendingvertically between its upper and lower edges and the peripheral edgethereof is positioned closely adjacent the inner walls of the reactionvessel 22 so that passage of chips into the bottom portion of saidreaction vessel 22 may be prevented.

For feeding the pressurized mixture of chips and liquid to the uppersurface of said plate, a tubular member 41 having its inner wallconcentric with and spaced from shaft 30 is mounted on the lower surfaceof said helical plate 32 extending downwardly therefrom, thus providinga central aperture between the upper and lower radial edges respectivelyof said helical plate and extending radially from said shaft to saidmember in the lower portion of the helical surface near said lower edge.Said movable member 41 is positioned closely within a fixed tubularmember 42 mounted in the lower end of reaction vessel 22 and extendsboth upwardly therefrom to overlap the downwardly extending edge ofmovable tubular member 41 and downwardly therefrom to provide aconnection to inlet line 24.

The screw conveyance 44 located near the top of the reaction vessel 22is adapted to remove drained wood chips therefrom, to move them throughconveyance housing 46, and to discharge them to the elongated receivervessel 48, of much smaller cross section dimension, say of the area ofvessel 22, connected through gas-tight fittings to the conveyancehousing 46, so that at least the top portions of said vessels are freelyinterconnected and so similarly maintained at high temperature andpres-' sure. In the bottom surface zone of the receiver vessel 48,generally defined as the volume below the illustrated flanged coupling,an upward facing, bladed agitator 50 is rotatably mounted andoperatively connected with a driving means 52, preferably an electricmotor. A bottom surface 54 generally conforms with the path of the lowerand outer edges of the rotatable blades, to define the lower extremityof the bottom zone. At least one orifice 56 is positioned in the bottomzone of the receiver vessel in the bottom surface 54 adjacent to andpreferably below the path of the bladed agitator 50 so that rotation ofthe bladed agitator causes each blade to wipe by the inlet to theorifice, preventing clogging. 'The orifice 56 is connected throughappropriate piping 58 to the atmosphere. A gate valve assembly 60 havinga controller 61 is preferably positioned in the orifice 56 for adjustingand closing its aperture, if desired. In the bottom zone, spaced apartfrom the orifice, there is a pressurized fluid inlet 70 which isconnected through valve 74 or 75 to a source of high pressure fluid, forexample, high pressure, steam taken, for example, from the top of thepressurized digester chamber, or preferably, to a source of cool liquid,such as dilute liquor or water, from line 76. Inlet 72 when utilized isused for the introduction of cool liquid sufliciently in advance ofdischarge in order that the downwardly moving wood chips will be moreeffectively cooled as they advance along receiver vessel 40 from inlet72 to discharge through orifice 56. Level sensor 53 connected to valves71 or 73 or controller 61 operates such elements as desired.

The operation of the apparatus is as follows: Wood chips are introducedinto pressurized reaction vessel 22, and, by the action of the particleadvancing means, are moved upwardly toward the outlet in successiveincrements as new material is added, while the heated cooking liquorelfects its cooking action in the cooking zone 46. Cooked wood chips arethus fed past upper strainer 43, through drainage zone 66 thereaboveand, at the upper end of said drainage zone, to conveyance 44. Theconveyance 44, extending between the two vessels, removes the drainedwood chips from reaction vessel 22 to establish and maintain apredetermined level of the top of the mass of wood chips above strainer43 defining the liquid level in vessel 22 to in turn define the upperend of the drainage zone, as well as to move them to the receiver vessel48, dropping them thereinto. The wood chips fall toward the bottom ofthe receiver vessel, thus building up a zone 49 with an upper level 49a,sensed by sensor 53 of drained wood chips conveyed thereto at an undulyhigh rate during non-uniform operation. The rotating driver 52 whirlsthe bladed agitator 50, maintaining the wood chips in the bottom zone 51of the receiver vessel 48 in a mobile homogeneous state and wiping theinlet of the orifice 56. The pressure diflerential across the orifice,attributable to the steam in the upper zone 47 of the receiver vessel 48and near atmospheric conditions at the orifice outlet causes wood chipsto flow outwardly therethrough. The zone 49 of wood chips interposedbetween the high temperature steam zone 47 in the upper portion of thereceiver vessel and the orifice reduces loss of steam by blowthrough(direct flow of steam to the orifice), as well as acting as an effectivetemperature insulating zone, so that the wood chips in the lower portionof vessel 48, at the lower end of zone 49, may be cooled as desired.

As the level of wood chips builds up in the receiver vessel 48 abovezone 49 constantly forcing the wood chips downward, the wood chips maybegin to compact and to offer great resistance to the rotation of thebladed agitator 50. When this results, either steam valve 74 or liquidvalve 75 or one or both of inlet valves 71, 73 and orifice valve 61 isopened by level sensor 53 and high pressure fluid is admitted throughinlet 70 and possibly inlet 72 as well to the bottom zone 51 of thereceiver vessel 48. The high pressure fluid at least partially equalizesthe pressure across the column of wood chips in zone 49, preventingfurther packing by the steam thereabove, and, additionally, forces someof the compacted wood chips out of the path of the rotating bladedagitator 50, lightening its load and allowing it to maintain properspeed to insure adequate agitation adjacent the orifice 56. Thus, levelsensor 53 operates to control the level 49a of the stored treated chipsby controlling input of fluid and output of pulp. By the addition of thefluid, the fluidity of the pulp in the bottom zone is increased. By thismeans, the rotating bladed agitator 50 effectively whittles away at thecolumn of wood chips partially held away by the steam.

According to the invention, it is preferred that the inlet be positionedclose to or within a region swept by the agitator blades, preferably inthe bottom surface 54 so as to clear material from between the blades ofthe agitator 50. It is also preferred that the inlet 70 be sufficientlyspaced apart from the orifice to prevent direct loss of fluid beforemixing with the wood chips has an opportunity to take place. Theprovision of additional inlet 72 permits more effective heat exchangewhen a cool liquid is introduced therethrough. It should be appreciated,however, that some of the benefits of this invention can be realized inpositioning the inlet in the peripheral casing surrounding the blades ofthe agitator, or in the portion of the bottom zone of the receivervessel 48 above the rotating agitator 50. It should likewise be apparentthat a wide variety of high pressure, low viscosity fluids will serve tolighten the agitator load.

As a particularly important aspect of the invention, especially insofaras fiber damage is concerned, cool water, either in pure form or in theform of dilute liquor at a temperature of sufliciently less than about212 degrees F. to cool the wood chips so that their temperature is lessthan 212 degrees F. after discharge, is particularly desirable in thatit functions to prevent flashing and resulting fiber damage as well asto aid in dilution in preparation for further treatment. Furthermore,the addition of such cool liquid to provide a cool zone 51 is mosteffective in preventing heat loss which does occur with the use ofsteam, and this is uniquely possible because the zone 49 of wood chipsin receiver vessel 48 acts as a temperature insulating zone so that ahigh temperature may be maintained in the upper zone 47 of said vesseland low temperature at the bottom thereof providing temperaturestability thereby as well, since the high temperature zone 47 above thelow temperature zone 49 prevents mixing by convection. Compressed airsimilarly avoids heat loss. Steam, however, may he used if loss of fiberstrength due to flashing is not 1mportant.

Referring now to FIG. 3, an ammeter, wattmeter, or the like placed inthe power line connected to the preferred electric motor agitator driveis connected so as to deliver a signal to an air pilot valve 92, of atype well known in the art. The ammeter signal is related to the energybeing consumed by the motor, which is an indication of the resistance torotation encountered by the agitator 50, in turn being proportional tothe compression of the wood chips and hence to the fluid pressurenecessary to be provided at inlets 70, 72. With an increase in theammeter signal, pilot valve 92 increases the air pressure invalve-actuating lines 94, which opens the valve 96. A decrease in thesignal similarly decreases the setting of the valve. By so utilizing thesystem of FIG. 3 in FIG. 1, continual automatic operation of theapparatus is achieved.

All examples herein set forth are merely illustrative of the inventionand are not to be interpreted as limiting the scope thereof.

What is claimed is:

1. In continuous pulping apparatus comprising a gen erally uprightpressurized elongated reaction vessel of generally uniform circularcross-sectional area for digesting wood chips, and means for feedingsubstantially continuously a Wood chip-liquid mixture into the lower endof said reaction vessel to maintain a compacted mass of wood chipswithin an elongated zone in the central and opposite upper end portionsthereof and advancing the wood chips upwardly through said zone at arate substantially independent of the movement of liquid in said vesselto treat said wood chips, that improvement consisting of dischargingmeans for discharging treated Wood chips from said pressurized reactionvessel, said discharging means including an upright pressurized pulpreceiver vessel having a cross-sectional area less than that of saidreaction vessel in a ratio of 10-50 to 1, and in free pressurecommunication with said reaction vessel, said pulp receiver vesselhaving a bottom surface with a bladed agitator rotatably mounted closelyadjacent to said surface and generally centrally thereof on a centralshaft to Wipe said surface, said bottom having a discharge orificethrough said surface and a fluid inlet through said bottom adjacent tosaid discharge orifice at a position spaced therefrom, means forrotating said agitator to wipe said surface across its area, valve meansfor controlling the opening of said orifice, valve means controlling theflow of said pressurized fluid through said inlet, means sensing theupper level of wood chips in said receiver vessel, conveyance meanslocated above said upper level of wood chips for moving drained woodchips from said reaction vessel to said pulp receiver vessel forcollection therein of substantially drained, treated wood chips, andmeans responsive to said level sensing means controlling said valvemeans for controlling the opening of said discharge to control saidupper level of orifice wood chips for continuous discharge of said chipsthrough said orifice While providing a flow of pressurized fluid to aidsaid discharge.

2. In continuous pulping apparatus as claimed in claim 1 wherein saidmeans responsive to said level sensing means also controls said valvemeans controlling the flow of pressurized fluid through said inlet.

3. In continuous pulping apparatus having a generally uprightpressurized elongated reaction vessel of generally circularcross-sectional area for digesting wood chips, means for feedingsubstantiallycontinuously a wood chip-liquid mixture into the lower endof said reaction vessel to maintain a compacted mass of wood chipswithin an elongated zone in the central and opposite upper end portionsthereof and advancing the wood chips upwardly through said zone at arate substantially independent of the movement of liquid in said vesselto treat said wood chips, and level means for establishing andmaintaining a level of said liquid adjacent the upper end of saidvessel, that improvement consisting of discharging means for dischargingtreated wood chips from said pressurized reaction vessel, saiddischarging means including an upright pressurized pulp receiver vesselin free pressure communication with said reaction vessel, said pulpreceiver vessel having a bottom surface with a bladed agitator rotatablymounted closely adjacent to said surface and generally centrally thereofon a central shaft to wipe said surface, an electric motor driving saidcentral shaft, means having a discharge orifice positioned in saidsurface radially outwardly of said central shaft beneath the path ofsaid agitator, and means having a fluid inlet in said surface adjacentto said discharge orifice at a position spaced therefrom, means forintroducing steam to said fluid inlet from said reaction vessel abovesaid level means for establishing and maintaining the liquid leveltherein, valve means for controlling the fiow of said steam through saidinlet responsive to the power consumed by said electric motor toincrease inflow upon increase in power consumption of said motor, andconveyance means located above said means for establishing andmaintaining the liquid level for moving drained wood chips from saidreaction vessel to said discharge vessel for collection therein ofsubstantially drained, treated wood chips and continuous discharge ofsaid chips through said orifice while providing a controlled flow ofsteam beneath said agitator to aid said discharge.

References Cited by the Examiner UNITED STATES PATENTS 2,008,635 7/35Brubacher 162-237 2,359,543 10/44 Branzell 162-237 2,938,824 5/60Richter 162-237 X DONALL H. SYLVESTER, Primary Examiner.

1. IN CONTINUOUS PULPING APPARATUS COMPRISING A GENERALLY UPRIGHTPRESSURIZED ELONGATED REACTION VESSEL OF GENERALLY UNIFORM CIRCULARCROSS-SECTIONAL AREA FOR DIGESTING WOOD CHIPS, AND MEANS FOR FEEDINGSUBSTANTIALLY CONTINUOUSLY A WOOD CHIP-LIQUID MIXTURE INTO THE LOWER ENDOF SAID REACTION VESSEL TO MAINTAIN A COMPACTED MASS OF WOOD CHIPSWITHIN AN ELONGATED ZONE IN THE CENTRAL AND OPPOSITE UPPER END PORTIONSTHEREOF AND ADVANCING THE WOOD CHIPS UPWARDLY THROUGH SAID ZONE AT ARATE SUBSTANTIALLY INDEPENDENT OF THE MOVEMENT OF LIQUID IN SAID VESSELTO TREAT SAID WOOD CHIPS, THAT IMPROVEMENT CONSISTING OF DISCHARGINGMEANS FOR DISCHARGING TREATED WOOD CHIPS FROM SAID PRESSURIZED REACTIONVESSEL, SAID DISCHARGING MEANS INCLUDING AN UPRIGHT PRESSURIZED PULPRECEIVER VESSEL HAVING A CROSS-SECTIONAL AREA LESS THAN THAT OF SAIDREACTION VESSEL IN A RATIO OF 10-50 TO 1, AND IN FREE PRESSURECOMMUNICATION WITH SAID REACTION VESSEL, SAID PULP RECEIVER VESSELHAVING A BOTTOM SURFACE WITH A BLADED AGITATOR ROTATABLY MOUNTED CLOSELYADJACENT TO SAID SURFACE AND GENERALLY CENTRALLY THEREOF ON A CENTRALSHAFT TO WIPE SAID SURFACE, SAID BOTTOM HAVING A DISCHARGE ORIFICETHROUGH SAID SURFACE AND A FLUID INLET THROUGH SAID BOTTOM ADJACENT TOSAID DISCHARGE ORIFICE AT A POSITION SPACED THEREFROM, MEANS FORROTATING SAID AGITATOR TO WIPE SAID SURFACE ACROSS ITS AREA, VALVE MEANSFOR CONTROLLING THE OPENING OF SAID ORIFICE, VALVE MEANS FOR CONTROLLINGTHE OPENING OF SAID ORIFICE, VALVE MEANS CONTROLLING THE FLOW OF SAIDPRESSURIZED FLUID THROUGH SAID INLET, MEANS SENSING THE UPPER LEVEL OFWOOD CHIPS IN SAID RECEIVER VESSEL, CONVEYANCE MEANS LOCATED ABOVE SAIDUPPER LEVEL OF WOOD CHIPS FOR MOVING DRAINED WOOD CHIPS FROM SAIDREACTION VESSEL TO SAID PULP RECEIVER VESSEL FOR COLLECTION THEREIN OFSUBTANTIALLY DRAINED, TREATED WOOD CHIPS, AND MEANS RESPONSIVE TO SAIDLEVEL SENSING MEANS CONTROLLING SAID VALVE MEANS FOR CONTROLLING THEOPENING OF SAID DISCHARGE TO CONTROL SAID UPPER LEVEL OF ORIFICE WOODCHIPS FOR CONTINUOUS DISCHARGE OF SAID CHIPS THROUGH SAID ORIFICE WHILEPROVIDING A FLOW OF PRESSUIRIZED FLUID TO AID SAID DISCHARGE.